Overview
The element gold (Au) has atomic number 79. It is a soft yellow metal, with the properties of metals. It doesn’t react with other elements easily, but forms alloys easily, with silver, copper, palladium, and other metals. It is a precious metal, with a long history in coins and jewelry. The properties of gold allow it to be used to treat some medical conditions.
Atomic Structure of Gold
Gold has only one stable isotope that occurs in nature, although a number of radioisotopes have been produced that decay rapidly. It has 79 protons and 118 neutrons in its nucleus. It is both heavy and dense. Radioactive isotopes of gold range from a half-life of over half a year to a number of nanoseconds.
Metallic Properties of Gold
Gold is the most malleable of all the metals. It can be beaten into sheets of gold leaf that are transparent. It can be drawn into thin wires or ductile. Pure gold is very soft, so it is often used in alloys with silver (electrum); palladium, nickel, or titanium (white gold); copper (rose gold); and many other metals. Gold forms an amalgam with mercury. It can be dissolved by aqua regia (nitro-hydrochloric acid) or cyanide, but otherwise resists corrosion.
Gold Coins and Jewelry
Gold has been used as a precious metal in coins and jewelry since prehistoric times. Many civilizations and countries have exchanged gold as currency, and people have hoarded gold as riches. Gold does not tarnish, so coins and jewelry do not lose their distinctive, bright yellow-gold color. Pure, or 24-karat gold, is too soft for many uses, so gold is often alloyed with other metals. Most gold in jewelry is 22-kt to 10-kt. Eighteen-karat rose gold is formed in an alloy of gold containing 25% copper, and higher karat alloys of palladium, titanium, silver, and gold are also highly prized by jewelers and collectors.
Other Uses of Gold
Gold is a highly versatile metal. Besides its use in jewelry, gold leaf can be used in space helmet visors, to coat electronic components, or within all forms of semiconductors and microconductors. It can be beaten into thread and used in fine embroidery or fabric, as “cloth of gold” or fine fil d’or (French for thread made of gold). Gold salts are injected to treat forms of arthritis or prepared in various forms to treat TB and other diseases. Radioactive isotopes of gold decay to attack cancer cells by nuclear medicine.
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